12th Class Biology Chapter 7 Cell Cycle Short Questions Answer
12th Class Biology Chapter 7 Cell Cycle Short Questions Answer
1.Define cell cycle?
The cell under goes a sequence of changes which involve period of growth replication of DNA followed by cell division.This sequence of changes is called cell cycle
2.How much time is required for cell cycle in case of human?
In the case of human cell average cell cycle is about 24 hours.
3.What do you know about chromatin?
Chromatin is a network of very fine threads which can be visualized but using histologic stains for DNA.
4.In higher plants instead of visible centriole what is present?
Higher plants lack visible centrioles instead they have its analogous region from which the spindle microtubules radiate.
5.What is metastasis?
The cells composing a malignant tumor or cancer divide more rapidly mostly invade surrounding tissues get into body circulatory system and set up areas of proliferation away from their site of original appearance.This spread of tumor cells and establishment of secondary areas of growth is called as metastasis.
6.When in plants and animals the meiosis takes place?
Meiosis takes place in diploid cells only in animals at the time of gamete formation while in plants when spores are produced.
7.Define crossing over?
It is the exchange of segments between non-sister chromatids of homologous chromosomes due to chiasmata formation.
8.What are the two significant happenings of meiosis?
Crossing over and random assortment of chromosomes are two significant happening of meiosis.
9.How many chromosomes do occur in male affected by Klinefelter’s syndrome?
Males with 48 chromosomes with 49 chromosomes and male with 47 chromosomes are also observed.
10.What are the symptoms of Turner’s syndrome?
The affected individuals have one missing X chromosomes.Individuals have female appearance with short stature webbed neck without ovaries and complete absence of germ cells.
11.What is apoptosis?
Internal programmer of events and sequence of morphological changes by which cell commits suicide is collectively called as apoptosis.
12.Name the different stages of interphase?
Interphase can further be divided into G1-phase S-phase and G2-phase.
13.What is G1-phase?
G1 is the period of extensive metabolic activity in which cell normally grows in size specific enzymes are synthesized and DNA base units are accumulated for the DNA synthesis.
14.What is Go?
Post-mitotic cell can exit the cell cycle during G1 entering a phase called Go and remain fore days weeks or in some cases even the life time of the organism without proliferating further.
15.What is S-phase of cell cycle?
Following the G1 is the S-phase during which the DNA is synthesized and chromosomes number is doubled.
16.What happens in G2-phasw?
In G2 phase the cell prepares for division i.e.energy storage for chromosome movements mitosis specific proteins RNA and microtubule subunits synthesis are accomplished.
It is the type of cell division which ensures the same number of chromosomes in the daughter cells as that in the parent cells.
18.What two conventional phases of Mitosis?
i)Karyokinesis which involves the division of nucleus. ii) Cytokinesis that refers to the division of the whole cell.
19.What is Mitotic apparatus?
The specialized microtubule structure including aster and spindle is called mitotic apparatus.
20.Name the microtubules which originate from centrioles?
Three sets of microtubules originate from each pair of centrioles i.e.astral microtubules kinetochore kinetochore microtubules and polar microtubules.
21.What events occur in prophase of mitosis?
Each chromosomes is visible having two sister chromatids attached at centromere.Towards the end of prophase nuclear envelope disappears and nuclear material is relesed is relesed in the cytoplasm neucleoli disappear.Mitotic apparatus is orgenized.Cytoplasm becomes more viscous.
22.What is kinetochore?
The centromere has special area the kinetochore with specitic base arrangement and special proteins where kinetochore fibres of mitotic apparatus attach.
23.What happens in Telopase of mitosis?
The centromere has special area the kinetochore with specific base arrangement and special proteins where kinetochore fibres of mitotic apparatus attach.
24.What is Phragmoplast?
At cytokinesis in plants a membrane structure called phragmoplast is formed from vesicles of golgi comples.These vesicles line up in the centre of the dividing cell where they fuse to form phragmoplast at the and of telophase.
25.Define cancer or what are cancer cells?
Any malignant growth r tumour from an abnormal and uncontrolled division of body cells is known as cancer.The cells involved in formation of tumour are called cancer cells.
26.What is Tumour?26.What is Tumour?
When cancer cells produce new cells which continue to proliferate in uncontrolled fashion an unwanted clone of cells called tumour is formed which can expand un-definitely.
27.What are two basic types of tumours?
Benign tumours ii) Malignant tumours
28.What is benign tumours?
Benign tumours are of small size and localized called benign.The cells in this type usually behave like the normal cells and have little deleterious effects.
29.What is malignant tumour?
The cells composing a malignant tumour or cancer divide more repidly mostly invade surrounding tissues get into the body’s circulatory system and set up areas of proliferation away from their site of original appearance.
30.How can you distinguish cancer cells from normal cells?
Cancer cells can be distinguished from normal cells because they are less differentiated than normal cells exhibit the characteristics of rapidly growing cells that is high nucleus to cytoplasm ratio prominenet nucleoli and many mitosis.
31.What are main causes of cancer?
Cancer is caused mainly by mutations in somatic cells.The cancer results from the accumulation of as few as three to as many as twenty mutations in genes that regulate cell division.
Meiosis is the special type of cell division in which the number if chromosomes in daughter cells reduces to half as compared to the parent cell.
33.How prophase of meiosis differs from that of mitosis?
This is very prolonged phase and differs from the prophase of mitosis,because in this chromosomes behave as homologous pairs.Each diploid cell has two chromosomes of each type one member from each parent.
34.What are homologous chromosomes?
The chromosomes which are similar but not necessarily identical are called as homologous chromosomes.
35.Name the substages of prophase I of meiosis?
Leptotene zygotene pachtene diplotene and diakinesis.
36.What is synapsis?
The pairing of homologous chromosomes during zygotene stage is called synapsis.
37.What is bivalent or tetrad?
Each paired but not fused complex structure of homologus chromosomes is called as bivalent or tetrad.
38.What is the duration of Pachytene leptotene and zygotene?
Pachytene may lasts for days weeks for days weeks or even years whereas leptotene and zygotene can last only for few hours.
39.What is chiasmata?
The paired homologous chromosomes repel each other and begin to separatebut still remain united by their point interchange which is called chiasmata.
40.What happens in Diakinesis?
The condensation of chromosomes reaches to its maximum.At the same time separation of the homologous chromosomes is completed but still they are united at one point more oftenly at ends.Nucleoli disappear.
41.What events occur in metaphase I of meiosis?
Nuclear membrane disorganize at the beginning of this phase.Spindle fibres orignate and the kinetochore fibres attach to the kinetochore of homologous chromosome from each pole and arrange bivalents at the equator.
42.How does anaphase I of meiosis differs from that of mitosis?
In anaphase I of meiosis the sister chromatids are not separated only homologous chromosomes get separated.While in anaphase of mitosis the sister chromatids are separated.
43.How meiosis maintains chromosome number constant generation after generation?
Meiosis usually takes place at the time of sexual cells formation thus reducing the number of chromosomes to half in each which is restored after fertilization and maintains chromosome number constant generation after genaration.
In non-disjunction chromosomes fail to segregate during Anaphase and Telophase and do not finish with equal distribution of chromosome among all the daughter nuclei.This results either increase in the number of chromosomes causing serious phusical social and mental disorders.
45.What is autosomal non-disjunction?
The non-disjunction in which autosomal chromosomes fail to segregate is called autosomal non-disjunction.
46.What is Downs Syndrome?
It occurs in man during which 21st chromosome fails to segregate resulting gemete with 24 chromosomes.This gamete fertilizes normal gemete the new individual will have 47 chromosomes.
47.Does Downs syndrome is related to the age of mother?
Yes the chances of teenage mother having downs syndrome child s one in many thousands forty years old mother one in hundred chance and by forty-five the risk is tree times greater.
48.What are apparent symptoms or effects of Downs syndrome?
The affected individuals have flat broad face squint eyes with the skin fold in the inner corner and protruding tongue mental retardation and defective development of central nervous system.
49.What is sex chromosomal non-disjunction?
The non-disjunction in which sex chromosomes fail to segregate is called sex chromosomal non-disjunction.
50.What is Necrosis?
The cell death due to tissue damage is called necrosis,during which the typical cell swells and bursts releasing the intracellular contents which can damage neighbouring cells and cause inflammation.
What is meant by cell cycle?
The sequence of changes in a cell involving period of growth, replication of DNA followed by cell division is called cell cycle.
Write down the two basic phases of cell cycle?
The two basic phases of cell cycle are the interphase and the mitotic phase.
Describe sub-phases of interphase.
These are the G₁-phase during which cell grows in size and synthesizes specific enzymes; S-phase during which DNA is synthesized and the chromosome number is doubled; G₂-phase during which the cell is prepared for division.
What are the durations of different stages of the human cell cycle?
These are mitosis, 30 minutes G₁, 9 hours; S-phase, 10 hours; and G₂, 4.5 hours.
Write down the duration of cell cycle in yeast cell?
The duration of cell cycle in yeast cells is only 90 minutes.
Define centrosome in an animal cell?
In an animal cell, the centrosome is the region of the cytoplasm surrounding the centrioles.
Differentiate between mitotic and meiotic cell division?
During mitotic cell division the number of chromosomes in the daughter cells remains the same as in the parent cell where as in meiotic cell division it is reduced to one half of the parent cell.
How do karyokinesis and cytokinesis phases of cell division differ?
Karyokinesis is the division of the nucleus which is followed by the division of the cytoplasm known as cytokinesis.
Name the phases into which nuclear division (Karyokinesis) can be distinguished for convenience?
Karyokinesis can be distinguished for convenience into four phases viz, prophase, metaphase, anaphase and telophase.
What are chromatids?
Due to the replication of DNA during interphase, each prophase chromosome consists of two coiled filaments which are known as the chromatids.
What is mitotic apparatus formed of in animal as well as in plant cells?
The mitotic apparatus in animal cells is formed of spindle, asters and centrioles where as in plant tells it consists of only the spindle.
Write down the chemical composition of the spindle fibers, including both the kinetochore fibers and the polar fibers?
The spindle fibers are chemically made of mainly a protein, the tubulin along with traces of RNA.
Explain equatorial plate in cell division?
At the metaphase stage the chromosomes attach themselves in the middle (equator) of the spindle in a circle looking like a plate, known as the equatorial plate.
What is karyotype in a cell?
The chromosomal set of an individual (or a species) with all its characteristics, such as number of chromosomes, their shapes, size and position of centromeres is called karyotype.
What is a telocentric chromosome?
A chromosome having the centromere located at its one end is called telocentric chromosomes.
What is the difference between the acrocentric and sub metacentric chromosomes?
The centromere of the acrocentric chromosome lies very near to one end with the result that one arm of the chromosome is very small or even imperceptible. In sub metacentric chromosome the centromere lies at some distance from one end so that the two arms of the chromosome are unequal.
How would you identify a metacentric chromosome?
In metacentric chromosome the centromere lies at the center and both arms of the chromosome are equal.
At which stage of mitosis do the chromatids separate as independent chromosomes?
The chromatids separate as independent chromosomes at the anaphase stage of mitosis.
How is the parent animal cell divided into two daughter cells at late telophase? OR How does cytokinesis take place in on animal cell?
At late telophase the actin and myosin at equatorial region of the cell get activated, form a contractile ring followed by a cleavage furrow which deepens dividing the parent cell into two daughter ones.
How does cytokinesis take place in a plant cell?
In the plant cell, a membranous partition called phragmoplast is formed at the equator of the spindle from vesicles which originate from the golgi complex during metaphase and fuse together at the end of the telophase. Later cellulose and pectin are deposited to form new cell wall.
Which kind of cell division is involved in asexual reproduction in plants and animals?
It is the mitosis which is involved in asexual reproduction in plants and animals.
Explain a tumour?
The tumour is a swelling a mass of abnormal tissue which resembles the normal tissue in structure but performs no useful function and grows at the expense of the body. The tumour may be benign/innocent or malignant causing metastasis. The malignant tumour is also called cancer.
Why are the ‘X’ and ‘Y’ chromosomes known as the sex chromosomes?
‘X’ and ‘Y’ chromosomes are known as the sex chromosomes because they help in the identification of the male and the female organisms.
What are the chromosomes other than the sex chromosomes known as?
They are called autosomes.
Non-disjunction is mistake which sometimes occurs during meiosis in which the homologous chromosomes of a pair (or more) fail to separate from each other.
What is Klinefelter’s syndrome?
Klinefelter’s syndrome is a hereditary defect in which a human male possesses an extra X-chromosome.
What is the cause of Down’s syndrome?
The cause of Down’s syndrome is the presence of an extra autosome in the cells of the affected person.
Write down the cause of Turner’s syndrome in human beings?
The cause of Turner’s syndrome is the absence of one X-chromosome in the afflicted human female whose sex chromosomes are XO.
Write down the effects of Klinefelter’s syndrome on the affected male humans?
The affected male humans become physically mature but remain sexually immature.
Internal programme of events and sequence of morphological changes by which cells commit suicide are collectively called as apoptosis.
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